Flame-retardant polypropylene resin composition

ABSTRACT

The present invention relates to a flame-retardant polypropylene resin composition comprising (A) polypropylene resin 20-60% by weight, (B) polyphenylene ether-based resin 1-50% by weight, (C) hydrogenated block copolymer of a vinylaromatic compound and conjugated diene, which mainly is based on vinylaromatic compound, 0.1-15% by weight, (D) aromatic phosphoric ester in phenol strucure 1-20% by weight, (E) polyammonium phosphate 1-20% by weight, and (F) pentaerythritol-based flame retardant auxiliary agent 0.1-13% by weight. The weight ratio of the aromatic phosphoric ester in phenol structure to the polyammonium phosphate is preferably 0.2-5.0. The composition has advanced flame-retardant and heat-resistant property, and processing property.

This application is a National Stage Application of InternationalApplication Number PCT/KR01/00898, published pursuant to PCT Article21(2).

TECHNICAL FIELD

The present invention relates to novel flame-retardant polypropyleneresin compositions, which have been improved in incombustibility andother physical properties. More specifically, the present inventionrelates to incombustible polypropylene resin compositions prepared bydispersing polyphenylene ether-based resin, phosphorus flame-retardantand flame-retardant auxiliary agent in the major component,polypropylene resin in a specific ratio.

BACKGROUND ART

Since they have excellent processability, chemical resistance, weatherresistance and mechanical strength, polypropylene resins have beenwidely used in various fields including household electrical appliances,building materials, interior decorative materials, automobile parts,etc. However, they need to be supplemented with a variety of organic orinorganic flame-retardants in order to obtain incombustibility requiredfor these uses.

Exemplary incombustible polypropylene resin compositions containing suchflame-retardants include compositions comprising polypropylene resin andhydrated inorganic compound such as magnesium hydroxide, aluminumhydroxide and hydrotalcite (See: Japanese Laid-open Publication Nos.53-92855, 54-29350, 54-77658, 56-25954, 57-87462 and 60-110738);compositions comprising polypropylene resin, polyethylene resin with amelt index of 0.01˜2.0, halogen compound (for example, decabromodiphenylether or dodecachloro-dodecahydromethanodibenzocyclooctene), andinorganic filler selected from the group consisting of stone powder,kaolin, celestite, silica and diatomite (See: Japanese Laid-openPublication No. 55-30739); and compositions comprising polypropyleneresin and either a reaction product, which is generated from a reactionbetween an aldehyde compound and a nitrogenous compound wherein ═C═O (or═C═S or ═NH) group is incorporated into ammonium phosphate (or aminephosphate) ring structure, or an oligomer (or polymer) of 1,3,5-triazinederivatives (See: Japanese Laid-open Publication Nos. 52-146452 and59-147050).

However, the compositions, which were prepared by adding inorganiccompound such as magnesium hydroxide to polypropylene resin so as toobtain highly incombustible resin composition, have been found to bepoor in their plasticity. On the other hand, the compositions preparedby adding decabromo phenyl-based compound to polypropylene resin arerelatively good in their plasticity and incombustibility, but aredisadvantageous in that they generate poisonous gases during secondaryprocessing or combustion.

In contrast, the compositions disclosed in Japanese Laid-openPublication Nos. 52-146452 and 59-147050 do not show the decline ofsecondary processing property as well as the production of corrosive andpoisonous gases. Also, these compositions exhibit the incombustibilityof V-0 at {fraction (1/16)} inch thickness when tested according to thevertical firing test protocol out of “COMBUSTIBILITY TESTS OF PLASTICMATERIALS FOR MACHINE PARTS” of UL Subject 94(Underwriters LaboratoriesIncorporation). Nonetheless, these compositions are inferior in thermalresistance and impact strength, so they are unsuitable to be used inmachine parts requiring these physical properties.

On the other hand, polyphenylene ether resins have been known as highlyefficient plastics having excellent incombustibility, thermalresistance, size stability, non-hydroscopicity and electric properties.Therefore, an improved resin composition, which would advance inplasticity, impact resistance, thermal resistance and incombustibilityand thus could be used in extensive areas, may be expected when mixing apolypropylene resin with a polyphenylene ether resin and thereby makingup for each other's demerits and making use of each other's merits. Forthis reason, various polyolefin/polyphenylene ether-based polymer alloyshave been vigorously proposed in the art. For example, U.S. Pat. No.3,994,856 describes blending of polyphenylene ether withpolystyrene-based hydrogenated block copolymer for the purpose ofimproving impact resistance and solvent resistance. U.S. Pat. No.4,145,377 discloses thermoplastic resin compositions, which wereenhanced in impact resistance and solvent resistance by blending eitherpolyphenylene resin or a mixture of polyphenylene resin andstyrene-based resin together with both a pre-mixture consisting of 20˜80weight parts of polyolefin and 80˜20 weight parts of hydrogenated blockcopolymer and hydrogenated block copolymer. U.S. Pat. Nos. 4,166,055 and4,239,673 teach improvement of impact resistance by blendingpolyphenylene ether with both hydrogenated block copolymer andpolyolefin. Similarly, U.S. Pat. No. 4,383,082 and European Patent No.115712 also teach improvement of impact resistance by blendingpolyphenylene ether with both polyolefin and hydrogenated blockcopolymer. Further, Japanese Laid-open Publication Nos. SHO 63-113058,SHO 63-225642, HEI 3-72512, HEI 4-183748 and HEI 5-320471, and U.S. Pat.No. 4,863,997 disclose resin compositions having advanced chemicalresistance and processability, which were prepared by adding aparticular hydrogenated block copolymer as a modifier to a blend ofpolyolefin resin and polyphenylene ether resin. In addition, JapaneseLaid-open Publication No. HEI 7-53859 discloses incombustible resincompositions prepared by adding halogen-containing phosphoric estercompound and antimony compound to a blend of polyolefin resin andpolyphenylene ether resin.

The polymer alloy compositions obtained from the above prior artsprovide improved resin compositions, which take advantages of polyolefinresin and polyphenylene ether resin concerning thermal resistance,mechanical strength and processability. However, these polymer alloycompositions are still poor in incombustibility, and therefore require alarge amount of flame-retardant, which results in significant decreasein mechanical strength. Meanwhile, Japanese Laid-Open Publication No.HEI 11-140245 describes preparation of thermoplastic incombustible resincompositions by adding an aromatic phosphoric ester compound and a1,3,5-triazine-based nitrogenous compound to a blend of polyphenyleneether resin and hydrogenated copolymer. In our test, however, thesecompositions did not succeed in showing incombustibility of UL94 V-0,and were found to have difficulties in ensuring practical thermalresistance because of steep decrease in thermal resistance.

DISCLOSURE OF THE INVENTION

A feature of the present invention is to solve those problems of theprior arts and to provide novel flame-retardant polypropylene resincompositions, which have been improved in incombustibility as well as inany other physical properties by mixing polypropylene resin withpolyphenylene ether-based resin having hindered phenol structure,aromatic phosphoric ester having hindered phenol structure andpolyammonium phosphate as a condensed phosphate, in a specific ratio,and further adding pentaerythritol as a flame-retardant auxiliary agentthereto.

Briefly, according to the present invention, there is providedflame-retardant polypropylene resin compositions comprising (A)polypropylene resin, which is the major component of the composition,20˜69% by weight, (B) polyphenylene ether-based resin 1˜50% by weight,(C) hydrogenated block copolymer, which is mainly based on aromaticvinyl compound, 0.1˜15% by weight, (D) aromatic phosphoric ester inphenol structure 1˜20% by weight, (E) polyammonium phosphate 1˜20% byweight, and (F) pentaerythritol-based flame-retardant auxiliary agent0.1˜13% by weight.

As used herein, “polypropylene” refers to propylene homopolymer as wellas propylene olefin block copolymer containing 50 wt. % or morepropylene unit.

In the resin compositions of the present invention, the polypropyleneresin (A) may be crystalline polypropylene homopolymer, or crystallinecopolymer consisting of propylene and one or more compounds selectedfrom the group consisting of ethylene, 1-butene, 1-pentene, 1-hexene,4-methylpentene, 1-heptene, 1-octene and 1-decene. Melt index of thepolypropylene resin is in the range of 0.3˜100 g/10 min (230° C., 2.16kg), preferably 0.5˜40 g/10 min. If the melt index of the polypropyleneresin is below 0.3 g/10 min, defects in appearance, such as a flow markon the surface of the molding product, occurs in the course of injectionmolding. Conversely, if the melt index of the polypropylene resin isover 100 g/10 min, impact resistance of the molding product becomeslower suddenly.

According to the present invention, any of the crystalline polypropyleneresins can be used regardless of its stereoregularity. However,crystalline polypropylene having an isotactic pentad fraction ofpreferably 0.80˜0.99, more preferably 0.85˜0.99, and most preferably0.90˜0.99 is preferred.

In the resin compositions of the present invention, amount of thepolypropylene resin (A) is 20˜69% by weight, and preferably 25˜63% byweight. If the polypropylene resin content is less than 20% by weight,plasticity and solvent resistance of the resin composition are inferiorin spite of relatively superior thermal resistance. Conversely, if thepolypropylene resin content is more than 69% by weight, thermalresistance of the resin composition is inferior in spite of relativelysuperior plasticity and solvent resistance, and thus the compositioncannot be used as thermal resistant materials.

According to the present invention, the polyphenylene ether-based resin(hereinafter, referred to as “PPE”) (B) is an essential component whichprovides thermal resistance and incombustibility to the resincompositions of the present invention. The polyphenylene ether-basedresin is made from hindered phenol monomers. The polyphenyleneether-based resin is one or more selected from the group consisting ofpoly(2,6-dimethyl-1,4-phenylene)ether,poly(2,6-diethyl-1,4-phenylene)ether,poly(2,6-dipropyl-1,4-phenylene)ether,poly(2-methyl-6-ethyl-1,4-phenylene)ether,poly(2-methyl-6-propyl-1,4-phenylene)ether,poly(2-ethyl-6-propyl-1,4-phenylene)ether,poly(2,6-diphenyl-1,4-phenylene)ether, copolymer ofpoly(2,6-dimethyl-1,4-phenylene)ether andpoly(2,3,6-trimethyl-1,4-phenylene)ether, and copolymer ofpoly(2,6-diethyl-1,4-phenylene)ether andpoly(2,3,6-trimethyl-1,4-phenylene)ether. Preferably,poly(2,6-dimethyl-1,4-phenylene)ether is used. Polymerization degree ofthe polyphenylene ether resin is not specifically limited, but the resinhaving an inherent viscosity of 0.2˜0.8(measured in chloroform solventat 25° C.) is preferred considering thermal stability and processabilityof the resin composition.

In the resin compositions of the present invention, amount of thepolyphenylene ether-based resin (B) is 1˜50% by weight, preferably 5˜45%by weight. If the polyphenylene ether-based resin content is over 50% byweight, thermal resistance of the resin composition is excellent butplasticity and solvent resistance are poor. Conversely, if thepolyphenylene ether-based resin content is below 1% by weight,plasticity and solvent resistance of the resin composition are increasedbut incombustibility and impact resistance are decreased.

The hydrogenated block copolymer (C) based on vinyl aromatic compound(hereinafter, referred to as “hydrogenated block copolymer) has astructure of A-B-A-B-A, wherein Block A corresponds to a polymer blockbased on one or more vinyl aromatic compounds, and Block B correspondsto a conjugated diene block based on one or more conjugated dienecompounds, wherein 45% or more of the conjugated diene compounds arelinked to the vinyl. This hydrogenated block copolymer plays a role inevenly dispersing the polyphenylene ether-based resin (B) in thepolypropylene resin (A).

The vinyl aromatic compounds constituting such hydrogenated blockcopolymer, for example, can be one or more selected from the groupconsisting of styrene, α-methyl styrene, vinyl toluene, P-tert-butylstyrene and diphenyl ethylene, and styrene is preferred. Thehydrogenated block copolymer is also commercially available. Forexample, Tuftec H1052 can be obtained from Asahi Chemicals Co., Ltd.

In the resin compositions of the present invention, amount of thehydrogenated block copolymer (C) is 0.1˜15% by weight, preferably 2˜10%by weight. If the hydrogenated block copolymer is contained over 15% byweight, thermal resistance of the resin composition is decreased. On thecontrary, if the hydrogenated block copolymer is contained below 0.1% byweight, impact resistance of the resin composition is reduced due tofailure in the efficient dispersion of the polyphenylene ether-basedresin in the polypropylene matrix.

The aromatic phosphoric ester (D) used in the present invention, whichhas phenol structure, can be exemplified by triphenyl phosphate, andother aromatic phosphoric ester compounds having hindered phenolstructure such as tri(2,6-dimethylphenyl)phosphate,tri(2,6-ditertiarybutylphenyl)phosphate, etc. Such phosphoric estercompound can be used solely or as a mixture. According to the presentinvention, use of a phosphoric ester compound having a molecular weightover 1500 should be avoided, because it hardly improves theincombustibility of the resin composition. Preferably, phosphoric esterhaving a melting point of 80° C. or more is used.

The polyammonium phosphate (E) used in the present invention isadvantageous in that: it produces not erosive gases, halogen gases andtoxic gases, but nonflammable gases (water vapor, CO₂, N₂, etc.) andcarbonaceous residue when degraded by contact with high temperaturecondition or flame. As the polyammonium phosphate, commerciallyavailable products, including Budit3076(Budenheim Co., Ltd.), SUMISAFE P(Sumitomo Chemicals Co., Ltd.) and Exolit422(Hoechst Co., Ltd.), can beused. Further, the polyammonium phosphate can be used with melamineadded and/or attached thereto. This melamine-added polyammoniumphosphate can be purchased from Chisso Co., Ltd. in the brand name ofTeraju C-60.

According to the present invention, the aromatic phosphoric estercompound having phenol structure and the polyammonium phosphate, incombination, serve as flame-retardants. At this time, weight ratio ofthe aromatic phosphoric ester compound to the polyammonium phosphate ispreferably 0.20˜5.0, more preferably 0.33˜3.0. If the weight ratio isout of this range, desired flame-retardant effect cannot be accomplishedand therefore a large amount of flame-retardant is required. In theresin compositions of the present invention, total amount of thearomatic phosphoric ester compound and the polyammonium phosphate shouldbe in the range of preferably 15˜30% by weight, more preferably 18˜25%by weight. If the total amount is below 15% by weight, sufficientflame-retardant effect cannot be obtained. On the other hand, if thetotal amount exceeds 30% by weight, thermal resistance of the resincomposition significantly decreases.

The pentaerythritol-based compound (F), which is used as aflame-retardant auxiliary agent in the present invention, can berepresented by the following formula (I):

In the above formula (I), R is —CH₂OH, and n is an integer ranging from1 to 5.

The pentaerythritol-based compound serves as a char promoter, whichhelps generation of char during combustion. For this purpose,dipentaerythritol or tripentaerythritol can be used. In the case thatpentaerythritol is used, its content of the resin composition is 0.1˜13%by weight, preferably 3˜12% by weight. If the content is less than 0.1%by weight, pentaerythritol cannot function as a flame-retardantauxiliary agent. Conversely, if the content is more than 13% by weight,thermal resistance of the resin composition declines significantly.

To the resin compositions of the present invention may be added furtheradditives such as plasticizer, thermal stabilizer, antioxidant and lightstabilizer. Organic or inorganic pigment and dye; inorganic filler suchas talc, silica and glass fiber; and flame-retardant auxiliary agentsuch as melamine and 1,3,5-triazine-based nitrogenous compounds can bealso added to the resin compositions of the present invention.

The resin compositions of the present invention are characterized inthat: (i) they produce no poisonous gases, which have been considered asan inevitable problem accompanied by the use of the conventionalflame-retardant; (ii) they show excellent incombustibility of UL94 V-0;and (iii) they have been enhanced in mechanical strength, such as impactresistance and heat resistance, and processability.

The resin compositions of the present invention can be prepared by theprocess as follows: polypropylene resin (A), polyphenylene ether-basedresin (B), hydrogenated block copolymer (C) based on aromatic vinylcompounds, aromatic phosphoric ester (D) having phenol structure,polyammonium phosphate (E), pentaerythritol (F) having the structure offormula (I), and the above mentioned various additives are filled in anagitating and mixing apparatus (for example, Hensel mixer, super mixeror tumbler mixer) in specified amounts, and mixed with agitating for1˜10 min, and then melted and mixed at 200˜290° C. by using a rollingmill or an extruder to provide pellets.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention can be more clearly understood with referring tothe following examples. It should be understood that the followingexamples are not intended to restrict the scope of the present inventionin any manner.

Measuring Protocols

1) Izod Impact Strength

Izod impact strength was measured according to the test standard ASTMD256 by using test pieces (3.2 mm in thickness) produced by injectionmolding.

2) Heat Deflection Temperature

Heat deflection temperature was measured according to the 18.5 kgf highload protocol of the test standard ASTM D648 by using test pieces (127.0mm in length, 12.7 mm in width, 6.4 mm in thickness) produced byinjection molding.

3) Incombustibility

Incombustibility was measured according to the vertical firing test(V-0) protocol out of “COMBUSTIBILITY TESTS OF PLASTIC MATERIALS FORMACHINE PARTS” of UL Subject 94(Underwriters LaboratoriesIncorporation). Thickness of the test pieces was {fraction (1/12)} inch.

EXAMPLE 1

In a Hensel mixer were filled 4.0 kg of polypropylene resin, i.e.,crystalline ethylene-propylene block copolymer having a melt index (flowamount of melted resin measured for 10 min at 230° C. under a load of2.16 kg) of 0.5 g/10 min, 3 kg of polyphenylene ether resin, 500 g ofhydrogenated block copolymer based on aromatic vinyl compounds, 1 kg oftriphenylphosphate, 1 kg of polyammonium phosphate, 500 g ofpentaerythritol, and 10 g of calcium stearate as an additive, and thenmixed for 3 min with agitating. The resulting mixture was melted andextruded through an extruder of 30 mm-caliber at 200˜260° C. to providepellets.

EXAMPLES 2˜3 AND COMPARATIVE EXAMPLES 1˜4

The same component compounds as in Example 1 were filled in a Henselmixer, except varying the respective amount of the aromatic phosphoricester having phenol structure and the polyammonium phosphate as shown inTable 1. Then, they were mixed with agitating, and the resulting mixturewas melted and extruded under the same condition as in Example 1 toprovide pellets.

The pellets obtained from Examples 1˜3 and Comparative examples 1˜4 weredried for 3 hrs at 100° C., and then molded through an injection moldingmachine, wherein maximum temperature of its cylinder had been adjustedto 230° C., to provide test pieces. The test pieces were subjected tothe tests for incombustibility and physical properties as describedabove. The results are shown in Table 1.

As can be seen from Table 1, all of Examples 1˜3, which were preparedaccording to the present invention, exhibited a heat deflectiontemperature over 80° C. as well as excellent incombustibility of V-0. Onthe contrary, all of Comparative examples 1˜4 exhibited excellentthermal resistance, but failed to achieve the incombustibility of V-0.

TABLE 1 (unit: 100 g) Comparative Comparative Comparative ComparativeExample 1 Example 2 Example 3 example 1 example 2 example 3 example 4(A) 40 40 40 40 40 40 40 (B) 30 30 30 30 30 30 30 (C) 5 5 5 5 5 5 5(D)-1 10 3.5 16.5 — 2 18 20 (D)-2 — — — — — — — (E)-1 10 16.5 3.5 20 182 — (E)-2 — — — — — — — (F) 5 5 5 5 5 5 5 (G)-1 — — — — — — — (G)-2 — —— — — — — Izod impact 14 11 8 6 8 20 23 strength (kg · cm/cm) Heatdeflection 91 93 86 97 95 83 80 temperature (° C.) Bending elastic 1635016750 15400 17200 16800 13200 11250 modulus (kg/cm²) IncombustibilityV-0 V-0 V-0 complete complete complete complete combustion combustioncombustion combustion Processability ◯ ◯ ◯ ◯ ◯ ◯ ◯ [Notes] Component(A): polypropylene resin(brand name: BB110P; Samsung General ChemicalsCo., Ltd.) Component (B): polyphenylene ether resin having hinderedphenol structure(brand name:P-401[poly(2,6-dimethyl-1,4-phenylene)ether]; Asahi Kasei Co., Ltd.,Japan) Component (C): hydrogenated block copolymer based on aromaticvinyl compounds(brand name: Tuftec H1052; Asahi Kasei Co., Ltd., Japan)Component (D)-1: Aromatic phosphoric ester having phenol structure(brandname: TPP[triphenylphosphate]; Daihachi Co. Ltd., Japan) Component(D)-2: Aromatic phosphoric ester having hindered phenol structure(brandname: PX-200[tri(2,6-dimethylphenyl)phosphate]; Daihachi Co., Ltd.,Japan) Component (E)-1: polyammonium phosphate(brand name: Budit 3076;Budenheim Co., Ltd., Sweden) Component (E)-2: melamine-coatedpolyammonium phosphaste(brand name: Teraju C-60; Chisso Co., Ltd.,Japan) Component (F): pentaerythritol(brand name: PER; Eujin ChemicalsCo., LTD.) Component (G)-1: nitrogenous compound(brand name: melamine;Samsung Fine Chemicals, Co., Ltd.) Component (G)-2: nitrogenouscompound, melamine cyanurate(brand name: MC610; Nissan Chemicals Co.,Ltd., Japan)

EXAMPLE 4

In a Hensel mixer were filled 3.7 kg of polypropylene resin, i.e.,crystalline ethylene-propylene block copolymer having a melt index (flowamount of melted resin measured for 10 min at 230° C. under a load of2.16 kg) of 0.5 g/10 min, 3 kg of polyphenylene ether resin, 500 g ofhydrogenated block copolymer based on aromatic vinyl compounds, 500 g oftriphenylphosphate, 1 kg of polyammonium phosphate, 1.3 kg ofpentaerythritol, and 10 g of calcium stearate as an additive, and thenmixed for 3 min with agitating. The resulting mixture was melted andextruded through an extruder of 30 mm-caliber at 200˜260° C. to providepellets.

EXAMPLES 5˜6 AND COMPARATIVE EXAMPLE 5

The same component compounds as in Example 4 were filled in a Henselmixer, except varying the respective amount of the polypropylene resinand the pentaerythritol as shown in Table 2. Then, they were mixed withagitating, and the resulting mixture was melted and extruded under thesame condition as in Example 1 to provide pellets.

The pellets obtained from Examples 4˜6 and Comparative example 5 weredried for 3 hrs at 100° C., and then molded through an injection moldingmachine, wherein maximum temperature of its cylinder had been adjustedto 230° C., to provide test pieces. The test pieces were subjected tothe tests for incombustibility and physical properties as describedabove. The results are shown in Table 2.

As can be seen from Table 2, all of Examples 4˜6, which were preparedaccording to the present invention to contain pentaerythritol, exhibiteda heat deflection temperature over 80° C. as well as excellentincombustibility of V-0. On the contrary, Comparative example 5exhibited excellent thermal resistance, but failed to achieve theincombustibility of V-0. These results suggested that pentaerythritolplayed an important role as a flame-retardant auxiliary agent.

TABLE 2 (unit: 100 g) Comparative Example 4 Example 5 Example 6 example5 (A) 37 44.9 32 42 (B) 30 30 30 30 (C) 5 5 5 5 (D)-1 5 10 20 10 (D)-2 —— — — (E)-1 10 10 10 13 (E)-2 — — — — (F) 13 0.1 3 — (G)-1 — — — — (G)-2— — — — Izod impact strength 16 17 12 20 (kg · cm/cm) Heat deflection 8997 98 99 temperature (° C.) Bending elastic 15800 17300 16900 16500modulus (kg/cm²) Incombustibility V-0 V-0 V-0 complete combustionProcessability ◯ ◯ ◯ ◯

EXAMPLE 7

In a Hensel mixer were filled 4.0 kg of polypropylene resin, i.e.,crystalline ethylene-propylene block copolymer having a melt index (flowamount of melted resin measured for 10 min at 230° C. under a load of2.16 kg) of 0.5 g/10 min, 3 kg of polyphenylene ether resin, 500 g ofhydrogenated block copolymer based on aromatic vinyl compounds, 1 kg oftriphenylphosphate, 1 kg of melamine-coated polyammonium phosphate, 500g of pentaerythritol, and 10 g of calcium stearate as an additive, andthen mixed for 3 min with agitating. The resulting mixture was meltedand extruded through an extruder of 30 mm-caliber at 200˜260° C. toprovide pellets.

EXAMPLES 8˜9 AND COMPARATIVE EXAMPLES 6˜8

The same component compounds as in Example 7 were filled in a Henselmixer, except varying amount of polypropylene resin, kind and amount ofaromatic phosphoric ester having phenol structure, and kind and amountof polyammonium phosphate as shown in Table 3. Then, they were mixedwith agitating, and the resulting mixture was melted and extruded underthe same condition as in Example 1 to provide pellets.

The pellets obtained from Examples 7˜9 and Comparative examples 6˜8 weredried for 3 hrs at 100° C., and then molded through an injection moldingmachine, wherein maximum temperature of its cylinder had been adjustedto 230° C., to provide test pieces. The test pieces were subjected tothe tests for incombustibility and physical properties as describedabove. The results are shown in Table 3.

As can be seen from Table 3, whether the phosphoric ester compound had aphenol structure or a hindered phenol structure, all of Examples 7˜9prepared according to the present invention exhibited a heat deflectiontemperature over 80° C. as well as excellent incombustibility of V-0. Onthe contrary, all of Comparative examples 6˜8 containing noflame-retardant auxiliary agent, pentaerythritol, failed to achieve theincombustibility of V-0, though they contained the flame-retardants,phosphoric ester having phenol structure and polyammonium phosphate.Moreover, addition of a nitrogenous compound as an alternativeflame-retardant auxiliary agent did not help to ensure theincombustibility of V-0.

TABLE 3 (unit: 100 g) Comparative Comparative Comparative Example 7Example 8 Example 9 example 6 example 7 example 8 (A) 40 40 40 35 35 35(B) 30 30 30 30 30 30 (C) 5 5 5 5 5 5 (D)-1 10 — — 10 20 — (D)-2 — 10 10— — — (E)-1 — 10 — 10 — 20 (E)-2 10 — 10 — — — (F) 5 5 5 — — — (G)-1 — —— 10 — — (G)-2 — — — — 10 10 Izod impact 20 21 26 12 13 9 strength (kg ·cm/cm) Heat deflection 93 98 100 102 92 104 temperature (° C.) Bendingelastic 17200 16800 16900 19100 15400 19700 modulus (kg/cm²)Incombustibility V-0 V-0 V-0 complete complete V-1 combustion combustionProcessability ◯ ◯ ◯ ◯ ◯ ◯

EXAMPLE 10

In a Hensel mixer were filled 2.0 kg of polypropylene resin, i.e.,crystalline ethylene-propylene block copolymer having a melt index (flowamount of melted resin measured for 10 min at 230° C. under a load of2.16 kg) of 0.5 g/10 min, 5.0 kg of polyphenylene ether resin, 500 g ofhydrogenated block copolymer based on aromatic vinyl compounds, 1 kg oftriphenylphosphate, 1 kg of melamine-coated polyammonium phosphate, 500g of pentaerythritol, and 10 g of calcium stearate as an additive, andthen mixed for 3 min with agitating. The resulting mixture was meltedand extruded through an extruder of 30 mm-caliber at 200˜260° C. toprovide pellets.

EXAMPLE 11 AND COMPARATIVE EXAMPLES 9˜10

The same component compounds as in Example 10 were filled in a Henselmixer, except varying the respective amount of the polypropylene resinand the polyphenylene ether resin as shown in Table 4. Then, they weremixed with agitating, and the resulting mixture was melted and extrudedunder the same condition as in Example 1 to provide pellets.

The pellets obtained from Examples 10˜11 and Comparative examples 9˜10were dried for 3 hrs at 100° C., and then molded through an injectionmolding machine, wherein maximum temperature of its cylinder had beenadjusted to 230° C., to provide test pieces. The test pieces weresubjected to the tests for incombustibility and physical properties asdescribed above. The results are shown in Table 4.

As can be seen from Table 4, all of Examples 10˜11, which were preparedaccording to the present invention to contain an adequate amount ofpolyphenylene ether resin, showed excellent thermal resistance andimpact resistance, and the incombustibility of V-0. On the other hand,in the case that the polyphenylene ether resin was added over 50% byweight, excessive extrusion load and injection load, and consequently,poor plasticity were resulted. Conversely, in the case that nopolyphenylene ether resin was added, incombustibility was too lowered toachieve the incombustibility of V-0.

TABLE 4 (unit: 100 g) Example Example Comparative Comparative 10 11example 9 example 10 (A) 20 69 15 70 (B) 50 1 55 — (C) 5 5 5 5 (D)-1 1010 10 10 (D)-2 — — — — (E)-1 10 10 10 10 (E)-2 — — — — (F) 5 5 5 5 (G)-1— — — — (G)-2 — — — — Izod impact strength 24 11 20 5 (kg · cm/cm) Heatdeflection 104 80 107 69 temperature (° C.) Bending elastic 17100 1320014200 13600 modulus (kg/cm²) Incombustibility V-0 V-0 V-0 V-1Processability ◯ ◯ X ◯

As can be seen in the above Examples and Comparative examples, thepolypropylene resin compositions of the present invention have so goodincombustibility as to exhibit the incombustibility of UL94 V-0. Inaddition, they produce no erosive or poisonous gases during molding orcombustion. Finally, they have been highly improved in physicalproperties including impact strength and thermal resistance, as well asin size stability. Therefore, they are useful for preparation ofelectrical appliances, automobile parts, building materials, interiordecorative materials, etc., which basically require these properties.

What is claimed is:
 1. An flame-retardant polypropylene resincomposition comprising (A) polypropylene resin 20˜69% by weight, (B)polyphenylene ether-based resin 1˜50% by weight, (C) hydrogenated blockcopolymer, which is mainly based on aromatic vinyl compound, 0.1˜15% byweight, (D) aromatic phosphoric ester having phenol structure 1˜20% byweight, (E) polyammonium phosphate 1˜20% by weight, and (F)pentaerythritol-based flame-retardant auxiliary agent 0.1˜13% by weight,wherein the weight ratio of the aromatic phosphoric ester having phenolstructure to the polyammonium phosphate is in the range of 0.2˜5.0. 2.The flame-retardant polypropylene resin composition according to claim1, wherein the polypropylene resin is crystalline polypropylenehomopolymer, or one or more compounds selected from the group consistingof propylene olefin block copolymers including ethylene, 1-butene,1-pentene, 1-hexene, 4-methylpentene, 1-heptene, 1-octene and 1-decene.3. The flame-retardant polypropylene resin composition according toclaim 1, wherein melt index of the polypropylene resin is in the rangeof 0.3˜100 g/10 min.
 4. The flame-retardant polypropylene resincomposition according to claim 1, wherein isotactic pentad fraction ofthe polypropylene resin is in the range of 0.80˜0.99.
 5. Theflame-retardant polypropylene resin composition according to claim 1,wherein the polyphenylene ether-based resin is one or more compoundsselected from the group consisting ofpoly(2,6-dimethyl-1,4-phenylene)ether,poly(2,6-diethyl-1,4-phenylene)ether,poly(2,6-dipropyl-1,4-phenylene)ether,poly(2-methyl-6-ethyl-1,4-phenylene)ether,poly(2-methyl-6-propyl-1,4-phenylene)ether,poly(2-ethyl-6-propyl-1,4-phenylene)ether,poly(2,6-diphenyl-1,4-phenylene)ether, copolymer ofpoly(2,6-dimethyl-1,4-phenylene)ether andpoly(2,3,6-trimethyl-1,4-phenylene) ether, and copolymer ofpoly(2,6-diethyl-1,4-phenylene)ether andpoly(2,3,6-trimethyl-1,4-phenylene)ether.
 6. The flame-retardantpolypropylene resin composition according to claim 1, wherein the totalamount of the aromatic phosphoric ester having phenol structure and thepolyammonium phosphate is in the range of 15˜30% by weight.
 7. Theflame-retardant polypropylene resin composition according to claim 1,wherein the pentaerythritol is represented by the following formula (I):

In the above formula (I), R is —CH₂OH, and n is an integer ranging from1 to 5.